1. Field of Use
The present invention relates generally to electrical safety devices and more particularly to a Leakage Detection and Interruption (LCDI) device having ignition containment features.
2. Description of Prior Art
Conventional electrical appliances typically receive alternating current (AC) power from a power supply, such as an electrical outlet, through a pair of conducting lines. The pair of conducting lines, often referred to as the line and neutral conductors, enable the electrical appliance, or load, to receive the current necessary to operate.
A power cable typically comprises at least two conducting lines through which current travels from the power source to the load. Specifically, a power cable typically comprises a power line and a neutral line. A metal sheath can be used to surround the power line and the neutral line in order to provide the power cable with arc sensing capabilities.
The connection of an electrical appliance to a power supply through a pair of conducting lines can create a number of potentially dangerous conditions. In particular, there exists the risk of ground fault and grounded neutral conditions in the conducting lines. A ground fault condition occurs when there is an imbalance between the currents flowing in the power and neutral lines. A grounded neutral condition occurs when the neutral line is grounded at the load.
Ground fault circuit interrupters are well known in the an and are commonly used to protect against ground fault and grounded neutral conditions. A ground fault circuit interrupter (GFCI) typically comprises a differential transformer with opposed primary windings, one primary winding being associated with the power line and the other primary winding being associated with the neutral line. If a ground fault condition should occur on the load side of the GFCI, the two primary windings will no longer cancel, thereby producing a flux flow in the core of the differential transformer. This resultant flux flow is detected by a secondary winding wrapped around the differential transformer core. In response thereto, the secondary winding produces a trip signal which, in turn, serves to open at least one of the conducting lines between the power supply and the load, thereby eliminating the dangerous condition.
While GFCI circuits of the type described above are well known and widely used in commerce to protect against ground fault and grounded neutral, conditions, it should be noted that a power cable is susceptible to other types of hazardous conditions which are not protected against by a conventional GFCI circuit. As an example, it has been found that one type of arcing condition can occur between one of the conducting lines and the metal sheath which surrounds the conducting lines. It should be noted that the presence of this type of arcing condition between either the power line and the metal sheath or the neutral line and the metal sheath can result in a fire or other dangerous condition.
When an electrical spark jumps between two conductors or from one conductor to ground the spark represents an electrical discharge through the air and is objectionable because beat is produced as a byproduct of this unintentional “arcing” path. Such arcing faults are a leading cause of electrical fires. Arcing faults can occur in the same places that ground faults can occur—in fact, a ground fault would be called an arcing fault if it resulted in an electrical discharge, or spark, across an air gap. Arc fault detection is typically accomplished by monitoring the electrical current flow into a load and comparing the profile of this current flow to a characteristic “signature' that arcing faults will exhibit it is known for ALCI enclosures to “burn up” during an internal fire or ignition creating extreme hazards and dangerous conditions.
In U.S. Pat. No. 7,525,777, to Aromin, V, incorporated herein by reference for all it discloses, new and improved safety circuits for a power cables are disclosed. The power cable includes two or more conducting lines and a metal sheath surrounding the conducting lines. The safety circuits sense the presence of an arcing condition between one of the conducting lines and the metal sheath, and in response thereto, opens at least one of the conducting lines between the power supply and the load.
Although a variety of safety circuits are available to shut down an ALCI is response to hazardous arcing conditions there is a need for an ALCI that can contain “burn up” during an internal fire through the use of fire retardant materials and structure located on the circuit assembly.